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What is the Microsoft Primary Interop Assembly?


The Microsoft Primary Interop Assembly is a collection of libraries created by Microsoft, and included in most installs of Microsoft Office. The PIA is used by the GMetrix software to communicate with the Microsoft Office software installed on your computer. Without the PIA installed, the GMetrix Software will be unable to function correctly.

Potential Problems and Errors

The following is a list of the most common errors that the GMetrix software encounters when the PIA is missing:

  • Tests will not start. After selecting a test, and clicking "Start" to begin the test, the GMetrix software closes without warning.
  • "Exception Has Been Thrown By The Target Of An Invocation" error when clicking "Next" after answering a question.
  • "The product you have selected is not currently installed on this machine; please select a different test" error. This can be caused by the missing PIA, or a missing addon. For the article about addons, click here


If you suspect that the PIA is missing, you can check by using the GMetrix Check Office App feature in the GMetrix Software.

  1. Launch GMetrix.
  2. In the lower left , click, "Options"
  3. Go to the Checks tab. The output shows Green Check Marks for the products that have the PIA working correctly.
  4. If you have an Office product installed on your computer, and there is a Red X next to that product, that product may be missing its PIA.

GMetrix 5.1

As of GMetrix 5.1 (and newer) the PIA files are no longer referenced by the software. Updating to 5.1 will fix any issues the software is having while communicating with the PIA files. You can download the latest software at gmetrix.net/download.